AND Contents of a Register

[burg]

Hi,

I'm trying to "AND" the contents of a register with values from 0 - 255. I'm not sure how to approach this. Here is what I have so far:

                     movlw	b'11100001'		
			andlw		PORTB	
			movlw		PORTB

I don't know what the contents of the top 3 bits are on PORTB, and I don't want to change them. I don't think my code will work, however, cause PORTB is not a literal. I could move the value of PORTB into W, but how do I do that? Does "movf PORTB" work without chopping the MSB off?

Thanks!

 

[Brevor]

Sure you can MOVF PORTB without losing anything.
I'm not really sure what you are trying to do but you can

movf PORTB,W ;move port b to W register.
andwf PORTB,F ;AND the contents of the W register with PORTB.
Is this what you are trying to do ?

 

[bananasiong]

you want to AND from 0 to 255, but you don't want the top 3 bits to be affected? Then you can only AND from 0 to 31 because 2^5 - 1 = 31.
you have to move PORTB to w
movf PORTB, w ;move the content of PORTB to w
andlw b'11100000' ;AND b'11100000' with w
movwf Store ;move the result to Store

but why you want to do this?

 

[atferrari]

AND ing PORT input through W register

Hola Burg,

Look what I do in a 16F877 for reading the upper nibble of PORTB (b7:b4)


MOVLW B'11110000' ;load mask for lower nibble in W
ANDWF PORTB,W ;read upper nibble - bit clear means key pressed - reading saved in W
MOVWF JOKER ;copy reading to aux file


Instead of my mask you put your values from 0 to 255.

Compare with the syntax of your code and revert if needed.

 

[bananasiong]

movf PORTB,W ;move port b to W register.
andwf PORTB,F ;AND the contents of the W register with PORTB.
Is this what you are trying to do ?

This is doing nothing isn't it? The same thing in the PORTB will be stored back to PORTB.

 

[Brevor]

This is doing nothing isn't it? The same thing in the PORTB will be stored back to PORTB.

I was just showing some examples of data moves between port B and W.
They were not meant to be used together.

 

[bananasiong]

I was just showing some examples of data moves between port B and W.
They were not meant to be used together.

oops sorry for misunderstanding..

 

[burg]

Sorry about the confusion. What I have is 7 LED's connected to PortB on a 16F88. 5 LED's act as a Tachometer, and the other 2 act as warning lights. I want 5 LED's to change according to RPM, yet I dont want the other 2 LED's to be changed due to the Tach.

I was just reading the datasheet and was confused, cause it mentions only number between 0 - 127 can be moved. But anyways, would this be fine:

movf PORTB,W
andwf b'11100001'
movwf REGISTER

As suggested by banaasiong. Would it work for my situation? Thanks!

 

[bananasiong]

Sorry about the confusion. What I have is 7 LED's connected to PortB on a 16F88. 5 LED's act as a Tachometer, and the other 2 act as warning lights. I want 5 LED's to change according to RPM, yet I dont want the other 2 LED's to be changed due to the Tach.

I was just reading the datasheet and was confused, cause it mentions only number between 0 - 127 can be moved. But anyways, would this be fine:

movf PORTB,W
andwf b'11100001'
movwf REGISTER

As suggested by banaasiong. Would it work for my situation? Thanks!

?? Did I? I have suggested this:

movf   PORTB, w
andlw  b'11100001'   AND Literal with w, store into w
movwf REGISTER

If you use andwf b'11100001', not b'11100001' ANDed with w, but the content of address 0x00E1 is ANDed with w.

 

[burg]

That certainly was an error on my part. Thanks again!

 

[Mike - K8LH]

It sounds like you want to preserve the upper 3 bits of PORTB then overwrite the lower 5 bits with LED data representing RPM, yes, no? If so, I would assume you have some variable with data in the 5 lower bits that represents the new LED RPM pattern and I would code it like this;

;
        movf    PORTB,W         ; get current PORTB
        andlw   b'11100000'     ; preserve upper 3 bits (in W)
        iorwf   RPMdata,W       ; add lower 5 bits from RPMdata (in W)
        movwf   PORTB           ; update PORTB with new RPM LED pattern
;